There are two main power sources of a LCD Driver (Liquid Crystal Display Driver): one is provided by an external power supplier for voltage Vdd, and another is generated by the LCD's internal circuit for voltage Vpp. And, the substrate voltage of the chip's PMOS inside the LCD driver must be higher than the voltages of source electrode and drain electrode, or the heavy leakage current will go through the source electrode or drain electrode to the substrate of PMOS to destroy the chip.
But in current general LCD driver's internal circuit, the output voltage is usually higher than the voltage that the power supplier provides after a period of running time. And for some applications of consumptive products, the output voltage of a running LCD driver may be higher or lower than the voltage that the power supplier provides.
Therefore, the substrate voltage of PMOS must be able to adjust dynamically to maintain the substrate voltage at the highest voltage value inside the chip.
Please refer FIG. 1, which shows the circuit of traditional technique that may modify the output voltage Vout to Vin or Vpp. But for some applications that need to generate two different output voltages to control different circuits, the circuit in FIG. 1 cannot reach this requirement because of its only one output voltage.
So, based on the weak point of traditional technique and with hard working, finally the applicant researches and designs the present invention named “A Control Circuit with Multiple Power Sources”.